Mask systems form an interface between a patient and apparatus providing a supply of pressurized air or breathing gas and are hence sometimes referred to as patient interfaces. In this specification, the words mask system and patient interface will be used interchangeably. Mask systems in the field of the invention differ from mask systems used in other applications such as aviation and safety in particular because of their emphasis on comfort. This high level of comfort is desired because patients must sleep wearing the masks for hours, possibly each night for the rest of their lives. Mask systems typically, although not always, comprise (i) a rigid or semi-rigid portion often referred to as a shell or frame, (ii) a soft, patient contacting portion often referred to as a cushion, and (iii) some form of headgear to hold the frame and cushion in position. Mask systems often include a mechanism for connecting an air delivery conduit. The air delivery conduit is usually connected to a blower or flow generator.
A range of patient interfaces are known including nasal masks, nose & mouth masks, full face masks and nasal prongs, pillows, nozzles & cannulae. Masks typically cover more of the face than nasal prongs, pillows, nozzles and cannulae. In this specification, all will be collectively referred to as patient interfaces or mask systems. Nasal prongs, nasal pillows, nozzles and cannulae all will be collectively referred to as nasal prongs.
An inherent characteristic of nasal masks is that they do not seal the mouth region. A number of patients thus find that during sleep when muscles relax, mouth leak may occur. Alternatively, some patients are naturally mouth breathers and thus find a nasal mask type patient interface ineffective. Mouth leak is undesirable as, among other difficulties, it may result in noise, increased treatment pressure to compensate for the leak or an increased load on the nasal passages and potentially nasal obstruction or a runny nose. Full face masks or nose & mouth masks address this issue by sealing around both the nose and the mouth.
Leak is a problem common to all designs of patient interface. Since nasal bridge anthropometry varies greatly between patients, the soft patient contacting portion or cushion must adapt to the shapes of individual patients. Typically, this is not achieved for the entire range of patients and some form of leak occurs. The problem is heightened during sleep when the jaw moves and the head position changes. This action can often serve to dislodge the mask and cause leak. Since leak can be noisy and results in less-effective treatment, users often compensate by tightening the headgear more than is desired. This is detrimental for patient comfort and can cause skin breakdown or irritation.
A further problem encountered by patients who are using full face, nasal or nose and mouth masks is that the portion of the patient interface that seals around the nasal bridge prevents the patient from wearing spectacles. Additionally, it may give the sensation of being closed in, leading to a feeling of claustrophobia, particularly when combined with a mouth-sealing portion. A further disadvantage is that any leaks that may occur can affect the sensitive area surrounding the eyes.
Thus, there is a need for an improved mask system that does not suffer from the above-mentioned drawbacks.